During the printing of printed sheets, the circumferential surfaces of the cylinders such as the impression cylinders, which guide the sheets, can come into contact with printing ink that has not dried completely. In the case of impression cylinders, which are disposed behind the turning device in perfecting presses, such contact is technologically required for producing sheets printed on both sides. In order to prevent the accumulation of printing ink on the circumferential surfaces of the impression cylinders, the circumferential surfaces of such impression cylinders are configured to be ink-repelling. This is achieved by means of the use of ink-repelling materials and/or by means of producing special rough structures, which have an ink-repelling effect and facilitate pulling the printed sheet from the impression cylinder.
DE 1 258 873 A1 discloses that the circumferential surface of an impression cylinder may be roughened by means of graining, anodizing, or sand-blasting and configured as a chrome surface. DE 42 07 119 A1 discloses a sheet-guiding impression cylinder mantle profile for an impression cylinder in sheet printing presses. The profile consists of lines that are distributed in a statistically uniform manner, forming the counter-impression surface, disposed plane-parallel to the impression cylinder axis. The lines demonstrate certain raster fineness. It is furthermore known from DE 199 14 136 A1 that a rough structure may be produced on the surface of a sheet-guiding cylinder, by coating it with plasma, and providing it with an organic, ink-repelling coating.
Since the impression cylinders are exposed to continuous wear during operation of th printing presses, because of the material wear caused by contact with the sheets to be imprinted, their ink-repelling properties gradually decrease. In the case of known impression cylinders, this results in a noticeable impairment of the printing quality after approximately four to five years of operation, making a replacement necessary. For technological reasons, the circumferential surface can be renewed only with great effort in the installed state.
In order to counter the disadvantages, based on another known solution to the problem, the impression cylinder is configured in such a manner by providing additional fastening devices, that an ink-repelling foil, acting as a counter-impression surface, can be fastened detachably to the circumferential surface of the impression cylinder. An impression cylinder of this type has a smooth surface. The thickness of the foil is taken into consideration when the circumference of the impression cylinder is dimensioned. In most cases, the foils, serving as covering for impression cylinders are made from the same materials as the circumferential surfaces of the counter-impression cylinders mentioned above, acting as counter-impression surfaces, and have the same rough structure.
A foil for this purpose is known, for example, from DE 39 31 479 A1. It consists of a chemically resistant, wear-resistant and incompressible backing layer, on which a silicone coating is applied. DE 40 36 252 A1 discloses a sheet-guiding foil as a covering for an impression cylinder of rotary offset printing presses for perfecting printing. One surface of this foil is constructed smooth and the other surface is provided with uniformly distributed spherical domes and a chrome layer that evens out the micro-roughness.
The mechanical engineering effort and expenditure for configuring the attachment devices and the unsuitability for retrofitting sheet-guiding cylinders are disadvantages of the systems consisting of an impression cylinder and a foil, in each instance.